1. Field of the Invention
The present invention relates to the field of treatments for cancer tumors. More particularly, the present invention relates to treatment of cancer tumors with 1,2,4-benzotriazine oxides contained in an aqueous buffered vehicle.
2. Reported Developments
1,2,4-Benzotriazine oxides are known compounds. U.S. Pat. No. 3,980,779 discloses 3-amino-1,2,4-benzotriazine-1,4-di-oxide compositions having the formula ##STR1## wherein one of R and R.sup.1 is hydrogen, halogen, lower alkyl, halo (lower alkyl), lower alkoxy, carbamoyl, sulfonamido, carboxy or carbo (lower alkoxy) and the other of R and R.sup.1 is halogeno, lower alkyl, halo (lower alkyl), lower alkoxy, carbamoyl, sulfonamido, carboxy or carbo (lower alkoxy), as antimicrobial composition used to promote livestock growth.
U.S. Pat., 5,175,287 issued Dec. 29, 1992 discloses the use of 1,2,4-benzotriazine oxides in conjunction with radiation for treatment of tumors. The 1,2,4-benzotriazine oxides sensitize the tumor cells to radiation and make them more amenable to this treatment modality.
Holden et al (1992) "Enhancement of Alkylating Agent Activity by SR-4233 in the FSaIIC Murine Fibrosarcoma" JNCI 84: 187-193 discloses the use of SR-4233, namely 3-amino-1,2,4-benzotriazine-1,4-dioxide, also known and hereinafter sometimes referred to as tirapazamine, in combination with an antitumor alkylating agent. The, four antitumor alkylating agents, cisplatin, cyclophosphamide, carmustine and melphalan, were each tested to examine the ability of tirapazamine to overcome the resistance of hypoxic tumor cells to antitumor alkylating agents. Tirapazamine was tested alone and in combination with varying amounts of each of the antitumor alkylating agents. When SR-4233 was administered just be,fore single-dose treatment with cyclophosphamide, carmustine or melphalan marked dose enhancement leading to synergistic cytotoxic effects on tumor cells was observed.
International Application No. PCT/US89/01037 discloses 1,2,4-benzotriazine oxide as radiosensitizers and selective cytotoxic agents. Other related patents include: U.S. Pat. Nos. 3,868,372 and 4,001,410 which disclose the preparation of 1,2,4-benzotriazine oxides; and U.S. Pat. Nos. 3,991,189 and 3,957,799 which disclose derivatives of 1,2.,4-benzotriazine oxides.
Members of 1,2,4-benzotriazine oxides have been found to be effective in the treatment of cancer tumors when used in conjunction with radiation therapy and chemotherapy.
Radiation therapy and chemotherapy, along with surgery, remain the three primary modalities in the treatment of cancer. Radiation therapy and chemotherapy function as alternatives to surgery in the primary control of a variety of neoplasms, where surgery is limited by anatomic consideration. Current knowledge demonstrates that higher cure rates and greater quality of life could be afforded to cancer patients if the effectiveness of radiation therapy and chemotherapy were improved.
One way to improve the effectiveness of radiotherapy or chemotherapy is to take advantage of the hypoxia that exists in tumors--one of the few exploitable difference between normal and tumor tissues. Abnormal development of blood vessels is characteristic of a large number of solid tumors. This abnormal capillary system often results in areas of hypoxia, transient or permanent. In general, hypoxia increases the resistance of a cell, normal or cancerous, to therapy. A method that augments the kill of hypoxic tumor cells (or limits the radiation damage to normal tissues) would improve the therapeutic index of radiation or chemotherapy.
The benzotriazine compounds have been developed to take advantage of this relative hypoxia within the tumor. Tirapazamine, the most promising member of the benzotriazine series to date, is bioreduced under conditions of hypoxia to an active intermediate. This active intermediate can induce DNA damage, which enhances the effects of radiation therapy or chemotherapy and is cytotoxic in its own right. Because adjacent normal tissues are not hypoxic, this bioreduction allows for selective cytotoxic effects on hypoxic tumor cells.
Research has indicated substantial superiority of the benzotriazines over nitroimidazole radiation sensitizers and other bioreductive agents in vitro as shown in Table I.
TABLE I ______________________________________ Hypoxic Cytotoxicity Ratios For Various Bioreductive Drugs In Vitro Hypoxic Cytotoxicity Ratio.sup.a Bioreductive Agent (and type) Rodent Human ______________________________________ Tirapazamine (Benzotriazine di-N-oxide) 75-200 15-100 RSU-1069 (Nitroimidazole/Aziridine) 75-100 10-20 Misonidazole (Nitroimidazole) 10-15 15 Porfiromycin (Quinone) 5-10 .about.10 Nitracrine (Nitroacridine) 7 -- Mitomycin C (Quinone) 1-5 1-2 ______________________________________ .sup.a Hypoxic cytotoxicity ratio = For equivalent levels of cell killing the ratio of the drug concentration required under aerobic conditions vs. under hypoxic conditions.
Tirapazamine, however, has the drawbacks of insufficient solubility in pharmaceutical vehicles suitable for parenteral administration as well as being unstable in such vehicles. It has been found that the solubility of tirapazamine in water is about 0.81 mg/ml, which would required a large volume of the solution, approximately, 1 liter, to be administered to a patient for providing the proper dose. Attempts to enhance the solubility using surfactants such as Tween 80, and polymers such as Pluronic F68, Povidone and Albumin were unsuccessful with minimal increase in solubility. Solubility enhancement with co-solvents was more successful, however, the proportion of co-solvents necessary to solubilize the expected minimum tolerated dose of tirapazamine would mean infusing significant quantities of co-solvents, for example, up to 120 ml propylene glycol as a 50% v/v propylene glycol/aqueous solution. This large volume of a co-solvent is undesirable in an injectable formulation and risks unwanted clinical affects in a patient.
Tirapazamine also lacks stability on shelf-life: complete degradation occurs after refluxing for less than four hours in 0.1N sodium hydroxide.
The present invention has as its main object to provide an aqueous infusable/injectable formulation which contains sufficient amounts of the anticancer tumor agent and is stable on shelf-life. During our extensive clinical studies of tirapazamine it was realized that without sufficient solubility and stability this very promising drug would not help the countless patients suffering from cancer tumor.